1. Field of the Invention
The present invention relates to an evaporator for evaporating a low temperature fluid through a heat transfer from a high temperature fluid to the low temperature fluid, and especially to an evaporator having a high evaporation efficiency.
2. Description of the Related Art
In general, an evaporator is used in a plant of electric generation by temperature difference, steam power, chemistry, food engineering and the like, a refrigerator and a heat pump. Such an evaporator can make heat exchange between high temperature fluid and low temperature fluid for the purposes of making change of phase of the low temperature fluid from a liquid phase to a gaseous phase. The conventional evaporator may be classified into a shell and tube evaporator, a plate type evaporator, a spiral type evaporator and the like. The plate type evaporator is generally used as an evaporator for evaporating the low temperature fluid through the heat of the high temperature fluid for example in a plant of electric generation by temperature difference. An example of the conventional evaporator is shown in FIGS. 4 and 5. FIG. 4 is an exploded perspective view illustrating essential components of the conventional evaporator. FIG. 5 is a schematic descriptive view of the conventional evaporator in an assembled condition.
The conventional evaporator 100 as shown in FIGS. 4 and 5 is provided with plural pairs of heat exchange plates 101, 102. In each pair, the heat exchange plate 101 is placed on the other heat exchange plate 102. Upper and lower guide rods 105, 106 held between a stationary frame 103 and a support rod 104 support the plural pairs of these heat exchange plates 101, 102. The plural pairs of the heat exchange plates 101, 102 are firmly held between the stationary frame 103 and a movable frame 107 that is mounted on the guide rods 105, 106. Two heat exchange passages A, B are formed on the opposite surfaces of each of the heat exchange plates 101, 102. A high temperature fluid 108 flows in the heat exchange passage A and a low temperature fluid 109 flows in the other heat exchange passage B so as to make heat exchange.
The above-mentioned heat exchange plates 101, 102 having a prescribed shape and a surface condition can be obtained by press-forming a plate-shaped material. Openings "a", "b", "c" and "d" through which the high temperature fluid 108 or the low temperature fluid 109 can pass, are formed at four corners of each of the heat exchange plates 101, 102. Packing members 111, 112 are placed on the surfaces of the heat exchange plates 101, 102, respectively, so as to prevent the heat exchanger fluid 108 and the working fluid 109 from flowing in a mixing condition. The heat exchange plates 101, 102 have the same shape, but the heat exchange plates 102 is placed upside down relative to the normal placement of the heat exchange plate 101.
The heat exchange plates 101, 102 serving as the heat transferring face has a pattern of irregularity (not shown) formed thereon in order to increase the heat transferring area and facilitate the heat transfer from the high temperature fluid 108 to the heat transferring face as well as the heat transfer from the heat transferring face to the low temperature fluid 109.
However, due to the above-described structure of the conventional evaporator, the inlet portion through which the high temperature fluid 108 flows toward a zone between the heat exchange plates 101, 102 serving as the heat transfer face is small relative to the size of the plates 101, 102 so that the high temperature fluid 108, which is supplied through the inlet portion, has a velocity distribution in the width direction of the plates 101, 102. As a result, a uniform flowing condition of the supplied high temperature fluid 108 over the entirety of the heat transferring face cannot be obtained, leading to a non-uniform flowing distribution. Accordingly, a uniform contact condition of the high temperature fluid 108 with the heat transferring face over its entirety cannot also be obtained, causing a problem of low heat transfer efficiency of the high temperature fluid to the heat transferring face although the heat transferring face is relatively large.